The goal of this research is to identify the managed care mechanisms that influence the changes in practice patterns associated with medical innovation. The existing literature suggests that the adoption and diffusion of medical innovations is the primary cause of rising health care expenditures. Therefore, understanding whether managed care is likely to alter permanently the underlying trends in health care cost growth requires understanding how managed care influences the process by which medical innovations are integrated into the delivery of health care services. We focus on changes in treatment patterns between 1994 and 1997 for patients with coronary artery disease (CAD) in four diverse delivery systems. These delivery systems include a fee-for-service plan, an IPA model HMO, and two mixed model HMOs, each comprised of a group/staff system and a system resembling a network model HMO. collectively they enroll over three million individuals. This project has three specific aims: 1. To identify factors that have contributed to changes in practice patterns for CAD patients and assess the role that technology has played in causing those changes. 2. To identify the attributes of the organization that may affect the extent to which practice patterns change over time and the rate at which new technology diffuese. 3. To identify and assess the strategies that organizations have pursued specifically aimed at influencing CAD related practice patterns, including those aimed at controlling diffusion of CAD related innovations. The research will be based on semi-structures interviews of physicians (generalists and specialists), administrators of medical groups, and plan administrators and will be guided by the results of an ongoing study measuring practice patterns changes for CAD related services.